The Superior Radiant Products SRP EvenGrow radiant heater uses two stages to soften the radiant output. With an end-to-end heat variance of less than 15 percent, the heater has a bottom clearance of 36 inches. The EvenGrow heater is available in rates from 40,000 to 100,000 btus per hour, lengths from 30 to 50 feet and in natural gas or liquefied petroleum gas.